Age-related macular degeneration (AMD) is a slowly progressing multifactorial disease involving genetic ab- normalities and environmental insults. AMD is the leading cause of blindness for Americans over age 60. As the population ages, the prevalence of AMD will reach a maximum risk rate of ~30% at age 75. As smoking increases the risk of AMD and there is a 20% higher incidence of smoking in veterans than in the general US civilian population, the VA system will have to provide care for potentially ?7 million AMD cases. The current concepts of AMD recognize that chronic oxidative stress and inflammation (including complement activation) can trigger pathological changes in RPE, Bruch's membrane (BrM) and choroid. However, what this scheme does not consider is the regionality of AMD. Damage does not start in one location to spread from there, but is triggered in many different locations. This suggests that damage occurs in susceptible areas, while delaying it in more resilient areas (sparing of the fovea). Our research is based on the premise that the RPE is a site of aging and disease. The RPE is an essential support cell of the retina; it is a source for the debris found in drusen and BrM; and th RPE cells form a network of cells, connected via gap junctions (GJ). Hence the RPE is a prime candidate to either spread or limit the stress-response within the posterior pole. Spreading of infor- mation, or the bystander effect, can be mediated by two different mechanisms: transfer of a secreted signal to the recipient (individual molecules or signals contained in exosomes); or the spread of information by means of communication via GJ. Here we will be guided by our overall hypothesis that exosome and GJ-mediated com- munication in RPE monolayers contribute of the bystander effect and mediate regionality of RPE damage. The susceptibility of individual cells to the bystander effects is thought to be determined by their metabolic profile. Hence we further hypothesize that the resting state of the individual cell within a network will determine is sus- ceptibility to stress. [[These questions will be investigated in RPE networks derived from ARPE-19 cells as well as induced pluripotent stem cell-derived RPE cells from AMD and control patients with low and high genetic risk factors for AMD]]. In Aim 1, we will determine the effects of messengers contained in exosomes in execut- ing the bystander effect in RPE cells. We have demonstrated that exosomes generated by oxidative stress can serve as signaling vectors for communication between donor and recipient cells in a complement-dependent manner. This mechanism will be explored further to determine the polarity of exosome formation, the activity of exosomes on global and single cell responses, and the process by which exosomes transfer information. Aim 2 is designed to determine the effects of GJ communication in executing the bystander effect. Our preliminary data has shown that local oxidative stress in a donor cell can trigger spread of information leading to changes in mitochondrial homeostasis in a limited number of connected recipient cells. This observation will be further extended to determine the signaling events in donor and recipient cells elicited by local stress as well as the metabolic baseline parameters in recipient cells that correlate with susceptibility to responding to information from a donor cell, and to examine potential messengers that mediate GJ communication.